Final answer:
Abnormal levels of Potassium (K+) can lead to cardiac arrhythmias and even death due to its critical role in cardiac muscle function and electrolyte balance.
Step-by-step explanation:
The electrolyte that can cause cardiac arrhythmias and even death when present at abnormal levels is Potassium (K+). Electrolyte balance is crucial for the function of the heart as well as other muscles and the nervous system. High potassium levels, known as hyperkalemia, can lead to dangerous changes in heart rhythm and are significant because they can impair the function of skeletal muscles, the nervous system, and most critically, the heart. Electrolyte imbalance, particularly of potassium, can lead to partial depolarization of cardiac cells, preventing the heart from relaxing after contraction, potentially causing it to stop pumping blood.